Biology subjects

Kneppers, A.

Publications and source records attributed to Kneppers, A..

4 recordsLinked to original sources

bioRxiv2025

The AMPKa2/PHF2 axis is critical for turning over lipid droplets during muscle stem cell fate

Lipid metabolism is a key process required for muscle stem cell (MuSCs) function during regenerative myogenesis. However, the molecular pathway responsible of such regulation is still unknown. Studies of lysine demethylase PHF2 have reported its critical role in lipid metabolism in pathological processes, although there are no data regarding its role during MuSC fate transition. Here we show that PHF2 controls lipid droplet homeostasis in MuSCs during regenerative myogenesis, by promoting the contact between lipid droplets and mitochondria. Consistently, in absence of PHF2, myocytes accumulate lipid droplets, leading to mitochondrial dysfunction and impaired regeneration. Interestingly, such phenotype is rescued by AMPK2-PHF2 phospho-mimetic mutant expression. Our findings provide evidence that PHF2 is part of AMPK2 signaling and underscore the critical role of AMPK2/PHF2 axis in regulating lipid droplets homeostasis during MuSC fate.

cell biology↗

bioRxiv2024

Polymeric nanoparticles delivery of AMPK activator 991 prevents its toxicity and improves muscle homeostasis in Duchenne Muscular Dystrophy

Muscular dystrophies, such as Duchenne muscular dystrophy (DMD), are caused by permanent muscle injuries leading to chronic inflammation. In that context, macrophages harbor an altered inflammatory profile that contributes to fibrosis through the secretion of the profibrotic cytokine TGF{beta}1. We previously showed that AMP-activated protein kinase (AMPK) activation reduces TGF{beta}1 secretion by macrophages and improves muscle homeostasis and muscle force in a mouse model of DMD. This makes AMPK an attractive therapeutic target for treating chronic inflammation and fibrosis in DMD. However, potent direct AMPK activators like compound 991 show strong adverse effects in vivo, preventing their direct use. Here, we encapsulated 991 into biodegradable polymeric poly(lactic-co-glycolic) acid (PLGA) nanoparticles for in vivo delivery, in an attempt to overcome toxicity issues. We show that 991-loaded PLGA nanoparticles retained drug activity on fibrotic macrophages in vitro, by reducing their secretion of TGF{beta}1. In the D2-mdx pre-clinical DMD mouse model, intravenously injected PLGA nanoparticles reached gastrocnemius and diaphragm muscles, which are the most affected muscles in this model. Chronic intravenous injections of 991-loaded PLGA nanoparticles decreased inflammation in both muscles, which was associated with fibrosis reduction and increase in myofiber size and muscle mass in the gastrocnemius. No impact on blood cell counts and liver enzymes was observed. These results demonstrate that nanomedicine is an efficient strategy to deliver AMPK activators in vivo to target inflammation and improve the dystrophic muscle phenotype.

pathology↗

bioRxiv2024

Impaired skeletal muscle regeneration induced by Cre recombinase activation in skeletal muscle stem cells

The value of the Cre-lox system in biology is well-recognized, which is reflected by its widespread use to assess the role of a gene in a specific tissue or cell-type. Not in the least, Cre recombinase expressed under the Pax7 promotor has been invaluable for the study of skeletal muscle stem cell (MuSC) biology. In this study, we aimed to systematically assess the effects of the genetic makeup of Pax7Cre mice and Tamoxifen (Tx) treatment on skeletal muscle regeneration. We demonstrate that Tx treatment per se does not affect skeletal muscle regeneration at 14 days post injury (d.p.i.) induced by cardiotoxin, but specifically worsened regeneration in two Pax7CreERT2 lines. Pax7 heterozygosity in Pax7CreERT2(FAN) mice resulted in a lower body mass and Tibialis Anterior (TA) mass, a higher number of fibers per section, and a lower number of Pax7+ cells than in Pax7CreERT2(GAKA) mice, but Tx treatment did not worsen these effects caused by Pax7 haploinsufficiency. In vitro, proliferation of Pax7CreERT2(FAN) MuSCs was impaired after 4-Hydrotamoxifen (4-OHT) treatment, while cell survival and differentiation remained unaffected. Together with a lower number of nuclei per fiber after Tx treatment in Pax7CreERT2(FAN) and male Pax7CreERT2(GAKA) mice, this may suggest an impaired MuSC pool expansion upon Cre activation. Yet, the in vivo MuSC pool was maintained in Pax7Cre mice at 14 d.p.i. Overall, our results directly show that Cre recombinase activity has an off-target effect on MuSCs, which warrants the use of Tx-treated Pax7CreERT2 mice as experimental controls in future studies, and demand caution in interpreting data using other controls in previous studies.

cell biology↗

bioRxiv2024

Metformin protects the heart against chronic intermittent hypoxia through AMPK-dependent phosphorylation of HIF-1α

Chronic intermittent hypoxia (IH), a major feature of obstructive sleep apnea syndrome (OSA), is associated with a more severe myocardial infarction. In this study, we performed RNA sequencing of cardiac samples from mice exposed to IH, which reveals a specific transcriptomic signature of the disease, relative to mitochondrial remodeling and cell death. Corresponding to its activation under chronic IH, we stabilized the Hypoxia Inducible Factor-1 (HIF-1) in cardiac cells in vitro, and observed its association with an increased autophagic flux. In accordance, IH induced autophagy and mitophagy that is decreased in HIF-1+/_ mice compared to wild-type animals suggesting that HIF-1 plays a significant role in IH-induced mitochondrial remodeling. Next, we showed that the AMPK metabolic sensor, typically activated by mitochondrial stress, is inhibited after 3 weeks of IH in hearts. Therefore, we assessed the effect of metformin, an anti-diabetic drug and potent activator of AMPK, on myocardial response to ischemia-reperfusion (I/R) injury. Daily administration of metformin significantly decreases infarct size without any systemic beneficial effect on insulin-resistance under IH conditions. The cardioprotective effect of metformin is lost in AMPK2 knock-out mice demonstrating that AMPK2 isoform promotes metformin-induced cardioprotection in mice exposed to IH. Mechanistically, we found that metformin inhibits IH-induced mitophagy in myocardium and decreases HIF-1 nuclear expression in mice subjected to IH. In vitro demonstrated that metformin induces HIF-1 phosphorylation, decreases its nuclear localization and subsequently HIF-1 transcriptional activity. Collectively, these results identify the AMPK2 metabolic sensor as a novel modulator of HIF-1 activity. Our data suggest that metformin could be considered as a cardioprotective drug in OSA patients independently of their metabolic status.

physiology↗